1.Grand central isn't even released yet
2.guess what features in regards to multi core/processor/GPGPU usage (also unreleased) Windows 7 will offer ... _the same as grand central_ ... minus the more fancy buzzword easily thrown around in web forums
3. i would recommend to actually look up what the current windows vista kernel actually can do what other OS kernel still can't do
Matter of fact is that most big ass corporations (using Germany´s big caps as reference) use windows server (kernel like to Vista, actually Intel Employees have posted how to convert Server to Workstation tutorial) not any UNIX variants. Obviously, these entities rely heavily on applications that are in dire need for multi core hardware support. If Windows really was behind the picture would be different.
Anyways, gone are the days of the MacPro as the least expensive platform for hardcore computing no matter which OS you opt to install. In Early 08 it was impossible to DIY a system at that former pricepoint.